Inorganic-organic hybrid materials are, in general, composites of the same or different kinds of materials, and include those referred to as blended materials, composites, microcomposites, nanocomposites, hybrids, microhybrids, nanohybrids, nanocomposite materials, molecular composites, molecular composite materials, and the like. A variety of such materials from those merely mixed to those bound at the nano-level, or even the molecular or atomic level, are being developed.
Recently, the structure or construction of the materials, i.e., voids inside the materials, such as micropores or mesopores, is controlled in addition to the composition of the organic and inorganic materials, to regulate various properties, such as mechanical strength, optical properties, solvent resistance, water resistance, gas permeability, gas absorption/desorption, refractive index, dielectricity, magnetism, fluorescence, electrical conductivity, biocompatibility, hydrophilicity/hydrophobicity, anticlouding property, and anti-rust property, as well as characteristics, such as moldability and processability, by compositing various materials. This results in development of materials exhibiting diversified functions.
Many of the inorganic-organic hybrid materials with a matrix of an organic polymer, wherein the inorganic component is uniformly dispersed in the organic polymer, are intended to provide improved kinetic properties, heat resistance, and the like properties, while characteristics of the organic polymer are conserved, such as moldability, light weight, corrosion resistance, and durability. The organic polymer may be polyamide, polystyrene, polypropylene, acrylic resins, epoxy resins, or the like. On the other hand, as the inorganic component, alkoxysilanes, layered clay minerals, metal oxides, fine metal particles, or the like are taken into consideration. Recently, new materials, such as fullerene and carbon nanotubes, are also considered for application as the inorganic component.
Many of the inorganic-organic hybrid materials with a matrix of an inorganic component, wherein organic molecules are carried on or bound to a matrix of a metal oxide obtained by a sol-gel method, are intended to improve the properties of the metal oxide, such as brittleness, transmittance, and optical characteristics, while the properties of the organic molecules are expressed. In such materials, organic molecules or low molecular weight oligomers are confined in an inorganic component matrix usually by means of relatively weak bonds, such as van der Waals force or hydrogen bonds.
Recent studies further go into preparation of inorganic-organic hybrid materials followed by removal of the organic component, to thereby control the configuration of the inorganic material, i.e., to make it porous or to regulate its pore size, or preparation of materials having unique structures, configurations, or mesoporosity using organic molecules as a mold.
As inorganic-organic hybrid materials having characteristic structures, there are proposed materials having various organic molecules intercalated between the layers of an inorganic layered material, such as graphite, clay minerals, swelling layered silicate, montmorillonite, transition metal chalcogen compounds, or zirconium phosphate. Studies are being made for improving the properties of these materials, such as photoelectric or catalytic functions, by means of the functional organic molecules carried between the layers of the inorganic layered material. Further, so called functionally graded materials are also studied, wherein the properties of the material are controlled inside by adjusting the ratio of the organic to inorganic components inside the material.
Common synthetic resins, such as acrylic, polycarbonate, and PET resins, are widely used in various fields including the IT field for their various excellent properties, such as transparency and shapability, but have problems in durability due to their insufficient surface hardness and heat resistance. In order to overcome this drawback, the synthetic resins are usually treated on the surface for improving the wear resistance. Typically, an inorganic or organic coating composition is applied on the surface of the synthetic resin and cured to form a film having good wear resistance.
As such a coating composition, Patent Publications 1 to 5 disclose compositions containing a hydrolytic condensate of organoalkoxysilane, colloidal silica, and other compounds, and Patent Publication 6 discloses a composition containing a hydrolytic condensate of tetraalkoxysilane and organotrialkoxysilane, and colloidal silica. Further, as a coating composition with improved adhesion, Patent Publication 7 proposes a composition composed of organotrihydroxysilane, colloidal silica, a polysiloxane-polyether copolymer, aliphatic alcohol, and a plurality of water-miscible polar solvents capable of eroding plastics, and Patent Publication 8 proposes a composition composed of organotrihydroxysilane essentially containing phenyltrihydroxysilane, colloidal silica, and a solid adjusting agent.
These coating compositions provide good durability when formed into a coating film on glass. However, when these coating compositions are formed into a film on a synthetic resin, in particular, with the content of colloidal silica in the coating composition being increased, or with tetrafunctional alkoxysilane being added for improving the wear-resistance, the resulting coating film may be cracked or peeled off the synthetic resin substrate in durability tests such as humidity resistance test, thermal shock test, outdoor exposure, and accelerated exposure in a sunshine weather meter.
Patent Publication 9 proposes a method for producing an inorganic-organic hybrid using polyurethane with hydrophilic soft segment, hydrolysable alkoxysilane, and optionally alcohol sol containing a catalyst dissolved in lower alcohol. Patent Publication 10 proposes a method for producing an inorganic-organic hybrid material by reacting a metal alkoxysilane having an isocyanate group with a polyol having a hydroxyl group at both terminals, and then with alkoxytitanium by sol-gel method.
Patent Publication 11 proposes a composite material composition containing, as a binder, a hydrolysate of mixed silane compounds containing an alkoxysilane having an alkyl group and an alkoxysilane having an epoxy group, combined with a short fiber inorganic filler or an organic filler, for improving weatherability, flexibility, wear resistance, heat resistance, or the like properties. Patent Publication 12 proposes a method for producing a resin composite material by forming, on the surface of a synthetic resin, a polyimide precursor layer using inorganic powder particles, such as of ceramics, metals, or glass, and polyamidic acid.
However, the inorganic-organic hybrids obtained by these prior art methods do not necessarily have sufficient film hardness, transparency, adhesion, or weatherability. Thus, development of inorganic-organic hybrid materials which solve these problems, are demanded.
Particularly in the art of optical materials, inorganic-organic hybrid materials are required to have: (1) adjustability of the refractive index over a wide range, (2) light transmittance over a wide wavelength range, (3) lighter weight compared to inorganic optical materials, (4) better heat resistance and stability compared to organic materials, and (5) better flexibility compared to inorganic optical materials. Thus, development of inorganic-organic hybrid materials having such properties is also desired.
In such inorganic-organic hybrid materials, it is important to control translucency and refractive index as basic properties. Specifically, the refractive index of an inorganic-organic hybrid material is controlled by introducing an inorganic component other than Si, i.e., Al, Ti, Zr, or the like, into the system to increase the refractive index by means of high electronic polarization of a metal element (see Non-patent Publication 1). Further, it is known that, in a transparent inorganic-organic hybrid material, the refractive index linearly increases with the increase in the content of the inorganic component in the Lorentz-Lorenz relationship.
In conventional inorganic-organic hybrid materials, the refractive index of an organic component was increased by adding an inorganic component, i.e., the refractive index was controlled by the content of the inorganic component. Since the refractive index increases proportionally to the increase in the amount of the inorganic component added, an increased content of the inorganic component is required for higher refractive index. However, it was hard to achieve a high refractive index with the characteristics of the organic substance being conserved, such as flexibility, transparency, and adhesion.
Zinc plating and zinc alloy plating are generally used for preventing rusting on iron materials or parts used in vehicles or building material products. However, the zinc-plated iron materials and parts, when used intact, easily gather white rust, which is zinc rust, so that an additional protective film should be formed thereon. Such a protective film is usually formed by chromating, which produces a chromate film of practical corrosion resistance easily at low cost. However, since chromating requires harmful sexivalent chromium, not only the treatment liquid, but also the sexivalent chromium eluted from the treatment liquid may have adverse effects on human body or on environment.
In view of this, a number of so called chromium-free treatment techniques have been proposed for preventing formation of white rust on zinc-based-plated steel sheets without chromating.
For example, Patent Publication 13 discloses a method of forming on the surface of a zinc-based-plated steel sheet a first layer of a zinc phosphate treatment film containing at least one element selected from the group consisting of Ni, Mn, and Mg at a coating mass of 0.2 to 2.5 g/cm2, and forming thereon an organic film mainly composed of at least one organic resin selected from the group consisting of ethylene, epoxy, urethane, and acrylic resins. However, the film obtained by this method does not have high corrosion resistance comparable to that provided by chromating.
Patent Publications 14 to 17 disclose methods of forming on the surface of a zinc-based-plated steel sheet a first layer of a zinc phosphate film containing Mg, and a second layer of an organic-inorganic composite film composed of an epoxy resin and powder or colloid of SiO2, Al2O3, ZrO2, or the like. The film obtained by this method has certain corrosion resistance. However, the method involves formation of two layers of the zinc phosphate film and the organic-inorganic composite film, and the steps such as rinsing and drying of the first layer before formation of the second layer, which is complex.
Patent Publications 18 and 19 disclose methods of forming a ceramics coating layer on the surface of a zinc-based-plated steel sheet by applying and drying a sol solution of an alkoxide of Si, Ti, or Al that has been prepared in the acidic or alkaline region. The film obtained by this method has certain corrosion resistance. However, the adhesion to the substrate and the flexibility of the ceramics coating film per se made from the alkoxide is not necessarily sufficient. Thus, when small vehicle parts, such as bolts, nuts, and hose clamps, are treated by these methods, cracks may form disadvantageously.
The conventionally proposed anti-rust coating materials discussed above hardly meet the requirements for an anti-rusting agent for zinc-plated steel sheets that may replace the conventional chromating, with respect to corrosion resistance, production process, and the like. Thus, there is a demand for development of a chromium-free anti-rust coating material which is capable of forming an anti-rust film not only excellent in corrosion resistance, but also excellent in adhesion to the substrate, film hardness, and flexibility.
Incidentally, Patent Publication 20 proposes a diol (meth)acrylate compound having a urethane bond. However, usefulness of this compound in an inorganic-organic hybrid material is not known.    Patent Publication 1: JP-53-111336-A    Patent Publication 2: JP-56-104972-A    Patent Publication 3: JP-57-80460-A    Patent Publication 4: JP-57-80460-A    Patent Publication 5: JP-59-68377-A    Patent Publication 6: JP-8-283661-A    Patent Publication 7: JP-56-862-A    Patent Publication 8: JP-60-79071-A    Patent Publication 9: JP-6-136321-A    Patent Publication 10: JP-9-291131-A    Patent Publication 11: JP-2000-119525-A    Patent Publication 12: JP-2005-146243-A    Patent Publication 13: JP-2001-105528-A    Patent Publication 14: JP-2001-131763-A    Patent Publication 15: JP-2004-27330-A    Patent Publication 16: JP-2004-232082-A    Patent Publication 17: JP-2004-232083-A    Patent Publication 18: JP-2001-64782-A    Patent Publication 19: JP-2006-63358-A    Patent Publication 20: JP-2006-151953-A    Non-Patent Publication 1: Proc. SPIE Vol. 3136 (Sol-Gel Optics IV), p 134-142 (1997)